add ui jwt workflow that includes high contrast

define a new workflow inteded to be used by any service that needs to
render a ui. this workflow includes state indicating if high contrast
styles should be used.

refs CNVS-31909, closes CNVS-31983

test plan:
- enable high contrast
- make sure rcs is enabled
- go to view with rce sidebar
- get the jwt from Authoriation header of requests to rcs
  - don't inclued "Bearer "
- open the canvas console, run:
  Canvas::Security.decrypt_services_jwt(
    Canvas::Security.base64_decode('<token here>')
  )
- make suer the token inclues use_high_contrast: true
- disable high contrast
- repeat, but  use_high_contrast should be false in the token

Change-Id: I8752ad534928081d2e4b8e8d748f8dd9897222a2
Reviewed-on: https://gerrit.instructure.com/90452
Tested-by: Jenkins
Reviewed-by: John Corrigan <jcorrigan@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Product-Review: Brent Burgoyne <bburgoyne@instructure.com>

lib/canvas/jwt_workflow.rb

@@ -42,5 +42,11 @@ module Canvas
         ) || false
       }
     end
+
+    register(:ui) do |_, user|
+      {
+        use_high_contrast: user.try(:prefers_high_contrast?)
+      }
+    end
   end
 end

lib/services/rich_content.rb

@@ -11,7 +11,7 @@ module Services
             user,
             context: context,
             real_user: real_user,
-            workflows: [:rich_content]
+            workflows: [:rich_content, :ui]
           )
         end
 

spec/lib/canvas/jwt_workflow_spec.rb

@@ -69,6 +69,24 @@ module Canvas
           expect(state[:usage_rights_required]).to be true
         end
       end
+
+      describe ':ui' do
+        before(:each) do
+          @u.stubs(:prefers_high_contrast?)
+        end
+
+        it 'sets use_high_contrast to true' do
+          @u.expects(:prefers_high_contrast?).returns(true)
+          state = JWTWorkflow.state_for([:ui], @c, @u)
+          expect(state[:use_high_contrast]).to be true
+        end
+
+        it 'sets use_high_contrast to false' do
+          @u.expects(:prefers_high_contrast?).returns(false)
+          state = JWTWorkflow.state_for([:ui], @c, @u)
+          expect(state[:use_high_contrast]).to be false
+        end
+      end
     end
   end
 end

spec/lib/services/rich_content_spec.rb

@@ -51,7 +51,7 @@ module Services
         ctx = stub("ctx", grants_any_right?: true)
         jwt = stub("jwt")
         Canvas::Security::ServicesJwt.stubs(:for_user).with(domain, user, all_of(
-          has_entry(workflows: [:rich_content]),
+          has_entry(workflows: [:rich_content, :ui]),
           has_entry(context: ctx)
         )).returns(jwt)
         env = described_class.env_for(root_account, user: user, domain: domain, context: ctx)